WoTLK Login issues (password)

Hi,

I created an account earlier today and used a password manager to generate a complex password, consisting of alphanumeric and special characters (the generated password is available upon request).

I was able to login onto the website, but I was unable to login into the game.
I just changed my password to be only normal letters 8 character password and now I'm able to login.

Is this a bug or intended behaviour? And if intended, maybe it might be nice to warn upfront of any limitations of password complexity?

It's a technical limitation of the client that cannot be resolved.